Voice Over Internet Protocol (VoIP) is rapidly gaining acceptance in place of conventional telephony, for long distance calls because generally toll charges can be reduced. Internet telephony providers offer no-cost or low-cost services such that subscribers can originate and receive calls from their computer. The subscriber with appropriate VoIP software installed, wears a headset connected to the sound card of a personal computer. On-screen menus facilitate the dialing process and the computer modem dials out to the telephone exchange of the user""s Internet Service Provider. In the interest of minimizing cost to the ISP subscriber, i.e. the calling party, such calls are most often dialed to a local Central Office. The ISP will route the call through the Internet to the Central Office nearest the called party thus avoiding or reducing long distance tolls.
In conventional telephony, cordless sets are replacing corded telephones for reasons of convenience and mobility. The cost of such cordless phones today is low and the frequency spectrum allocation sufficient for the broad consumer market. Newer cordless handsets may come equipped with a headset jack for the added facility of hands-free operation. The headset is sometimes included with the phone or may be sold separately. The headset interface is generally from a 2.5 mm xe2x80x9cstereoxe2x80x9d plug at the end of the headset cord to a mating jack at the cordless handset. Informally manufacturers have standardized on the following connections for the plug and jack: tip to electret mic, ring to earphone receiver and sleeve to ground.
Just as the Internet is an international medium, little encumbered by national boundaries, so is VoIP becoming popular internationally. For users of VolP, the reduction of international toll charges is even more significant. Frequency allocation for cordless telephony varies by country or broader region, however. For a manufacturer to offer a product intended for cordless computer telephony, the product must be designed specifically for each set of frequency standards. In the United States for instance, CFR Title 47, Part 15 permits unlicensed operation at 46/49 MHz, 902-928 MHz and 2.4 GHz. China has a 45/48 MHz frequency allocation, France 26/41 MHz, New Zealand 34/40 and so on (see Reference 1, Motorola MC 13109 Universal Cordless Telephone IC). Moreover voltage and frequency standards for AC power vary by region, as do AC plug and socket configurations, placing an additional burden on the design of a cordless telephone.
Certain single purpose wireless headsets for interfacing to a computer are available, but they sell for several times the price of a cordless phone and product selection is limited. The wireless medium used is either diffuse IR or low power RF or magnetic induction. Exemplary units are sold by Andrea Electronics (AWS100 headworn mic using diffuse IR) and Emkay Innovative Products (RF-3296 using RF from mic to base and magnetic induction from base to headphone). They are not mainstream consumer electronic appliances and do not enjoy the cost advantage of high volume cordless phone production.
In one embodiment of the invention there is provided an interface apparatus interposed between a cordless telephone base unit and a personal computer sound card. Such interface emulates a Central Office connection with respect to the telephone and a mic and speaker connection with respect to the computer sound card. The apparatus is suitable for all cordless telephones regardless of frequency allocation standards because the interface occurs at the RJ-11 modular jack of the cordless phone base, normally intended for connection to a CO line. Differences in telephone line regulations that exist among countries are accounted for with no burden of complexity to the user of the present invention. The interface comprises active and passive circuits perform two-wire-to-four-wire conversion and signal conditioning. Local loop current may be obtained from batteries or a suitable AC power adapter.
In another embodiment of the invention there is provided a xe2x80x9cself poweredxe2x80x9d interface apparatus interposed between a cordless telephone base unit and a personal computer sound card. The interface operates as disclosed above, but without batteries or any concern about AC voltage, frequency or plug variations at the point of use. Instead, loop current is derived from one of the Universal Serial Bus receptacles at the PC. Such USB ports are found on most desktop and notebook computers manufactured since 1997. The USB standard assures that 5 V at 100 mA will be available for a downstream device at the moment of connection. Thus the computer telephony interface apparatus is configured to operate universally with the prevailing cordless telephone standards at the point of use and with no AC power adapter. A further benefit for this embodiment is obtained in connection with a notebook computer: total independence from AC mains when the laptop PC is operating with batteries and the cordless phone base is powered from a spare battery in the charging cradle. An exemplary cordless phone with spare battery provision (in the base unit) and a headset jack (in the handset) is V-Tech model vt1901.
In a third embodiment of the invention, a USB apparatus communicates with and is powered by the USB port to provide cordless headset operation for Internet telephony. Because this USB link to the computer is digital, it obviates the need for mic and speaker connections at the computer; no sound card is required. The USB interface performs the analog to digital and digital to analog conversion instead. The simulated telephone line from the interface apparatus operates with the cordless phone base as described above. With only two cords to connect, USB and RJ-11, this embodiment is simpler for the user.
It will be understood by those of ordinary skill in the art that any consumer telephone set, corded or cordless, with or without a headset jack will operate with the interface to be disclosed in further detail below, just as any telephone, FAX, modem, etc. will operate with any CO line. Such operation is advantageous for persons interested in VoIP but not comfortable with RF devices or headsets and who may prefer a traditional telephone. It will become evident that the invention is additionally suited for other uses: bringing voice to and from the computer for speech recognition, command and control, text to speech and so forth, independent of the modem and the Internet. No interface circuit change is required for such voice enabled applications with any of the embodiments disclosed, only the appropriate software is needed.
All embodiments of the invention are distinctly different from phone line simulators. Such products (see Reference 2, Viking Electronics DLE-200B Two Way Phone Line Simulator) are intended to perform as a rudimentary Central Office for demonstration purposes between two telephone sets. They provide dialtone and ringing voltage (which are not needed here) but do no two-wire-to-four-wire conversion or signal conditioning to carry voice between the user""s telephone set and the processor in the PC. Said differently, they do nothing to enable VolP or speech recognition.